use black wash..i like tamiya panel line accent color....but you can make your own....roughly a 10 to 1 mixture of black paint to thinner. It will run into crevices and leave high spots uncolored. Works good....ive even used craft paint thinned with water for this

Yes whatever you use as a "wash" must be thin and it will flow into the low spots and crevices. Take a tissue immediately and give the high spots a gentle swipe to remove any wash that has not settled in. This washing the grille makes a big difference in your finished model as I've seen two models same year and make side by side and you can surely see the one with the detailed grille.